1. Field of the Invention
This invention relates to methods and apparatuses for manufacture and inspection of semiconductor devices such as semiconductor chips encapsulated in packages.
2. Description of the Related Art
In general, semiconductor devices such as semiconductor chips are sealed and enclosed in packages, wherein internal ends of leads are connected with semiconductor chips by bonding wires, while external ends of leads are exposed outside of the exteriors of packages. That is, semiconductor chips, bonding wires, and internal ends of leads are all combined together and are integrally sealed within resins corresponding to packages.
FIG. 29 shows an example of a conventional manufacturing process of a semiconductor device, wherein a semiconductor chip 1 is mounted on a stage 6 of a frame 8, in which the prescribed number of leads 2 are arranged. Herein, pads 1a of the semiconductor chip 1 are connected with internal ends 2a of the leads 2 by bonding wires 3. Thus, a frame assembly 9 is produced and is set into a mold unit 100.
The mold unit 100 comprises a mold body 111 consisting of split molds 111a and 111b, which are split and vertically combined together, a cavity 112 formed inside of the mold body 111, and a pair of a runner 114 and a gate 115 that are used for injection of a resin, which is solidified to form a package. The split molds 111a and 111b are controlled in temperature and are also capable of holding external ends 2b of the leads 2 in an airtight manner by a mold drive apparatus (not shown). The cavity 112 is formed in a prescribed shape defining the exterior configuration of a package enclosing a semiconductor device. The runner 114 and the gate 115 form a passage for injecting unhardened thermosetting resin compounds (hereinafter, simply referred to as resin) into the cavity 112, so that they are formed and arranged along a split plane between the molds 111a and 111b. Specifically, one end of the runner 114 is communicated with a heating pot having a plunger (not shown), and the gate 115 is opened at a prescribed position of the cavity 112.
The aforementioned frame assembly 9 is set into the mold unit 100, which is then closed. Then, a resin is injected into the cavity 112 by way of the runner 114 and the gate 115, so that the cavity 112 is completely filled with the resin. Thereafter, the injected resin is gradually hardened in the cavity 112 at prescribed temperature, which is maintained for a while. After completion of hardening of the resin, the mold unit 100 is opened, so that the frame assembly 9 sealed with the resin is extracted therefrom. The external ends 2b of the leads 2 are subjected to cutting so that the frame assembly 9 is separated from the frame 8. Thus, it is possible to produce a semiconductor device enclosed in a resin package.
The aforementioned manufacturing method may have a drawback in the resin filling process in which during the injection of the resin, the bonding wires 3 are deformed inside of the cavity 112. Specifically, in the resin filling process in which the resin is injected into the cavity 112 from the gate 115, the bonding wires 3 that are normally comprised of very thin metal wires are pressed by flows of the resin and are deformed or twisted in the cavity 112. This may cause defective contacts, short-circuits, and breaks of the bonding wires 3 as well as unwanted occurrence of voids in the resin. Occasionally, the bonding wires 3 may be exposed outside of the exterior surface of the resin.
Japanese Unexamined Patent Publication No. Hei 10-189631 discloses an example of a method for preventing bonding wires from being exposed outside of the exterior surface of a package. This publication teaches pressing of bonding wires in the cavity as shown in FIG. 28, wherein a cavity modifying portion 220 is additionally provided with respect to a mold unit 220 consisting of split molds 211a and 211b, which are combined together to form a cavity 212 therein. Specifically, the cavity modifying portion 220 is arranged for the upper mold 211a of the mold unit 200 and is descended down into the cavity 212, so that top portions of bonding wires 3 are regulated in heights prior to resin injection. In this state, a resin is injected into the cavity 212 via a resin flow passage 221 that is formed to penetrate through the cavity modifying portion 220. After filling the cavity 212 with the resin but before completion of hardening of the resin in the cavity 212, the cavity modifying portion 220 is pulled upwards to a prescribed height corresponding to the surface of a package, which causes an unfilled space formed inside of the cavity 212. Then, such a space is further filled with the resin. In this method, however, the bonding wires 3 are pressed by flows of the resin into the cavity 212, so that they may be deformed or twisted to cause unwanted contacts, short-circuits, and breaks of the bonding wires as well as occurrence of voids in the resin. In addition, it may be unrealistic to inject the resin into the cavity 212 via the resin flow passage 221 formed in the cavity modifying portion 220 because of the thermosetting property of the resin, which is hardened inside of the cavity 212 and is also irreversibly hardened inside of the resin flow passage 221.
Through studies on causes of deformations of bonding wires inside of the cavity of the mold unit, we the inventors have ascertained a main cause of deformations of bonding wires, which will be described with reference to FIG. 29. During the process of injecting the resin into the cavity 112 whose space is gradually filled with the resin, the resin having a high viscosity presses the semiconductor chip 1 together with the stage 6 of the frame 8 (not shown), so that the semiconductor chip 1 is forced to be moved from the prescribed position thereof. Such unexpected movement of the semiconductor chip 1 in the cavity 112 causes a bonding wire 3X to be partially exposed on a side wall of the package and also causes a bonding wire 3Y to be twisted in the cavity 112, which in turn cause unwanted contacts, short-circuits, and breaks of bonding wires as well as occurrence of voids in the resin. These defects of bonding wires may be detected as defective products; however, they can be eliminated in manufacture by conduction inspections detecting short-circuits and/or breaks. When the number of defective products increases, the productivity is noticeably reduced. In addition, not all defective products are always detected by normal conduction inspections, and some of them may be shipped as good products, for which defectiveness will be indicated or claimed after the shipment. In that case, manufactured products are greatly reduced in reliability.